Coenzyme Q (ubiquinone), a dietary supplement, is a vitamin-like substance which is used to treat congestive heart failure and other cardiac problems, including heart ailments and diseases such as congestive heart failure, as well as a number of other conditions including high blood pressure, mitochochondrial disorders, including mitochondrial encephalomyopathy, anoxia, lactic acidosis, strokelike symptoms, neurodegenerative diseases, Kearns-Sayre syndrome and Alper's disease, among others. Coenzyme Q is the best known of a group of lipophilic quinones which have the capacity to transfer reducing equivalents or electrons within a lipid phase of cellular membranes. Reduced benzoquinones in general are effective reductants for oxygen or lipid radicals. Early studies showed that reduced coenzyme Q is an effective antioxidant. See, Mellors and Tappel, 1996, J. Biol. Chem., 241: 4353-4356. Reduced coenzyme Q now appears to function as part of a complex chain of antioxidant activity.
An important role of coenzyme Q can be in reduction of radicals of .alpha.-tocopherol and ascorbate formed when these antioxidants are oxidized by oxygen or carboxyl radicals. There are no enzymes for direct reduction of tocopheryl radical or external ascorbate radical, but there are enzymes in all membranes which can reduce coenzyme Q and the reduced coenzyme Q can reduce the tocopheryl or ascorbate radicals to restore tocopherol or ascorbate. Without the support of enzymes to reduce coenzyme Q, the reduced coenzyme Q would not be a very effective antioxidant because the semiquinone formed by interaction with lipid or oxygen radicals is readily autooxidized with formation of a superoxide radical.